A ventilation member is installed on a casing that accommodates electric components for an automobile, such as lamps, motors, sensors, and an ECU. Such a ventilation member has the function of ensuring ventilation between the interior and the exterior of the casing, the function of easing a change in pressure inside the casing caused by a temperature change, and the function of inhibiting the entrance of foreign matter into the casing. Examples of such a ventilation member are disclosed in JP-A-2001-143524 and JP-A-10-85536.
For example, a ventilation member 60 disclosed in JP-A-2001-143524 is formed of a cover part 61 in the shape of a bottomed cylinder, a cylindrical body 62 made of rubber, and a ventilation membrane 63 as are shown in FIG. 12A and FIG. 12B. The cylindrical body 62 has a diameter slightly smaller than that of the cover part 61, and the ventilation membrane 63 is disposed so as to close one of the openings of the cylindrical body 62. By fitting in the cylindrical body 62 inside the cover part 61 from the ventilation membrane 63 side, ventilation channels are defined between the inner peripheral surface of the cover part 61 and the outer peripheral surface of the cylindrical body 62 and between the bottom surface of the cover part 61 and the ventilation membrane 63. By inserting a cylindrical opening part 50a formed in the casing 50 into the cylindrical body 62, the ventilation member 60 as described above can be installed on the casing 50.